# std::experimental::barrier

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< cpp‎ | experimental

Defined in header `<experimental/barrier>` |  |
class barrier; |  | (concurrency TS)

The class `std::experimental::barrier` provides a thread-coordination mechanism that allows a set of participating threads to block until an operation is completed. Unlike std::experimental::latch, barriers are reusable; once the participating threads are released from a barrier's synchronization point, they can reuse the same barrier.

A barrier has a completion phase, which is executed by one of the participating threads once all threads in the set of participating threads arrive at the synchronization point. The `arrive_and_wait` and `arrive_and_drop` calls synchronize with the start of the completion phase; the end of the completion phase synchronizes with the returns from all calls blocked by its completion.

For `std::experimental::barrier`, the completion phase is empty. std::experimental::flex_barrier allows the user to control the completion phase with a function object.

The set of participating threads for a `barrier` constructed for `num_threads` threads is the first `num_threads` threads to arrive at its synchronization point after construction. The same set of threads (except for threads that called `arrive_and_drop()`) must arrive at the `barrier` each cycle.

### Member functions

(constructor) | constructs a `barrier` (public member function)
(destructor) | destroys the barrier (public member function)
operator= [deleted] | not copy-assignable (public member function)
arrive_and_wait | arrive at the synchronization point and block (public member function)
arrive_and_drop | arrive at the synchronization point and remove the current thread from the set of participating threads (public member function)

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